This Mentored Research Scientist Development Award (K01) will provide Dr. Heather A. Pines with the training and experience needed to facilitate her transition toward research independence in HIV prevention science. Dr. Pines' career development plan is designed to augment her training in epidemiology and allow her to: 1) develop expertise in social network analysis, 2) acquire skills in the use of genetic sequence analysis methods to identify HIV transmission clusters (i.e., individuals with genetically related HIV infections), 3) obtain further training in the ethical conduct of research, and 4) build the sklls necessary for a successful academic career. These training goals will be achieved through didactic courses, workshops, hands-on research, and mentoring from an interdisciplinary team of experts. Global disparities in resource allocation to HIV prevention services may limit the promise of recent breakthroughs in HIV prevention science, particularly among vulnerable substance using populations, such as men who have sex with men (MSM), in low- and middle-income countries (LMIC). Innovative research that integrates social network and genetic sequence analysis methods to direct the delivery of biomedical HIV prevention strategies to individuals at greatest risk may help maximize their impact, control costs, and facilitate their implementation in the context of limited prevention resources. To this end, the overall objective of Dr. Pines' research project is to inform the development of comprehensive HIV prevention programs that leverage information on sexual network characteristics to interrupt HIV transmission among MSM in LMIC. The project will be embedded in a NIDA study among MSM in Tijuana, Mexico (R01DA037811; PI: Patterson), to capitalize on its research infrastructure and the expertise of its bi-national collaborators, and provide Dr. Pines with the opportunity to apply her newly acquired skills in social network and genetic sequence analysis. Pilot data suggest elevated rates of substance use and associated sexual risk behaviors may be driving the HIV epidemic among MSM in Tijuana. Thus, understanding the impact of substance use on sexual network characteristics and HIV transmission dynamics among MSM will be a major focus of this research. Specifically, the project aims to: 1) examine the influence of mean degree (number of male anal intercourse partners), the degree distribution, and sexual mixing patterns on overall sexual network structure among MSM; 2) identify individual, sexual network compositional, and socio-contextual factors associated with degree; and 3) determine whether sexual mixing patterns are associated with HIV transmission cluster membership. Findings from this project will be critical to Dr. Pines' development of an R01 proposal that integrates epidemiologic, social network, and genetic sequence analysis methods to advance HIV prevention science. These training and research activities will position Dr. Pines as the only researcher in the Division of Global Public Health at the University of California, San Diego with this unique skill set and enable her to develop an independent research career.